Hydrophilic gels that contain up to 95 percent water have been known for some time. Some of the early hydrogels were prepared by irradiation crosslinking and exhibited smooth, non-tacky surfaces. Later developments included hydrogels having interesting surface characteristics, such as adhesiveness, tackiness or non-stringiness. These hydrophilic gels can be manufactured into different forms including sheets and a number of applications have been disclosed which utilize their unique characteristics. U.S. Pat. No. 5,143,071 lists a number of such hydrogels and specifically discloses polyvinyl pyrrolidone and polyethylene oxide hydrogels formed from aqueous solutions which are cross-linked by radiation dosages of 0.5 to 4.5 Mrads.
Many of these hydrogels are used as wound dressings. In one embodiment, the hydrogel is used as a film which acts as a barrier to protect the wound from external contamination, thus promoting healing. Water soluble drugs can be added to these films and these drugs can migrate though the hydrogel film without disruption of the film's bacterial barrier properties (See, e.g., U.S. Pat. No. 3,419,006). A number of hydrogel sheets adapted for use in medical electrode applications are produced commercially, wherein the use of electric current enhances the transfer of the drug through the film.
Although many examples of hydrogels and resulting products, such as medical electrode assemblies, are known, these prior materials suffer from one or more undesirable characteristics that limit or, in some cases, preclude their utility as wound dressings, drug delivery systems, medical electrodes or the like. In particular, these previous materials can dry out rapidly, become brittle when cooled or easily lose their adhesive surface characteristics with the slightest over-exposure to crosslinking radiation.
There is a need for hydrogel products which overcome the disadvantages of the prior art. In particular, there is a need for deep wound dressings, such as for treatment of ulcers, in the form of flexible, non-stringy, cohesive hydrogels which can be applied in a relatively fluid state and which forms a gel within the wound cavity to protect the wound and promote healing and which can later be removed as an integral component without affecting the healing process. The present invention provides a number of compositions which can satisfy this need.